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Fair Value of Financial Instruments - Reconciliation of Level 3 Financial Instruments (Details) - Level 3 - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ 16		$ 39
Contracts added from acquisitions		(1)		(1)
Total gains/(losses) — realized/unrealized included in earnings		(16)		(26)
Cash received		0		(1)
Purchases		(10)		(12)
Transfers into Level 3		113		130
Transfers out of Level 3		14		(13)
Ending balance		116		116
Gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets or liabilities still held		(18)		(30)
Debt Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		18		19
Contracts added from acquisitions		0		0
Total gains/(losses) — realized/unrealized included in earnings		1		1
Cash received		0		(1)
Purchases		0		0
Transfers into Level 3		0		0
Transfers out of Level 3		0		0
Ending balance		19		19
Gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets or liabilities still held		1		1
Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 73	(2)	$ 38	20
Contracts added from acquisitions		(1)		(1)
Total gains/(losses) — realized/unrealized included in earnings	52	(17)	74	(27)
Cash received		0		0
Purchases	8	(10)	16	(12)
Transfers into Level 3	25	113	33	130
Transfers out of Level 3	(6)	14	(9)	(13)
Ending balance	152	97	152	97
Gains (losses) for the period included in earnings attributable to the change in unrealized gains or losses relating to assets or liabilities still held	$ 36	$ (19)	$ 27	$ (31)

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- Definition

Fair Value, Net Derivative Asset (Liability) Measured On Recurring Basis, Unobservable Inputs Reconciliation, Acquisition

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No definition available.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount of unrealized gain (loss) recognized in income for derivative asset (liability) after deduction of derivative liability (asset), measured at fair value using unobservable input (level 3) and still held.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

Amount of gain (loss) recognized in income from derivative asset (liability) after deduction of derivative liability (asset), measured at fair value on recurring basis using unobservable input (level 3).

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Amount of purchases of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlements of financial instrument classified as a derivative asset (liability) after deduction of derivative liability, measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfers of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset) out of level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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